It is already known to control the movement of articles on a live roller conveyor by a driven belt or its equivalent which is moved into and dropped out of driving engagement with rollers that maintain a fixed position relative to the driven belt. Such an arrangement is disclosed by De Good in U.S. Pat. No. 3,724,642 of Apr. 3, 1973 where a pressure-type lifting means raises the driven belt into roller driving contact, and loss of pressure drops the driven belt out of roller driving contact. The action of the lifting means is controlled by sensor rollers in association with time delay valve means. A similar conveyor drive control arrangement is disclosed in Inwood et al in U.S. Pat. No. 3,768,630 of Oct. 30, 1973. It is also known to arrange article carrying rollers in a conveyor system where the rollers are normally resiliently lifted away from a driven belt having a fixed elevation so that the weight of articles depress the rollers and effect conveyance thereof. Such an arrangement is shown by Pipp in U.S. Pat. No. 3,612,247 of Oct. 12, 1971, and it includes an inflatable member to elevate the depressed rollers in the event an article is blocked and cannot move forward.
Live roller conveyors are known to have group roller braking provisions, such as the tension means of Fleischauer U.S. Pat. No. 3,621,982 of Nov. 23, 1971 which is actuated to apply a friction restraint on a group of rollers of sufficient magnitude to cause slippage in the roller drive means. An alternate braking arrangement is disclosed by Werntz U.S Pat. No. 4,006,815 of Feb. 8, 1977.